In order to satisfy the demand for wireless data traffic that is increasing after popularization of the 4th-generation (4G) communication system, efforts for developing an improved 5th-generation (5G) communication system or a pre-5G communication system have been made. For this reason, the 5G communication system or pre-5G communication system is called a beyond 4G network communication system or a post Long Term Evolution (LTE) system.
It is considered to achieve a 5G communication system in millimeter wavebands (mmWave) (for example, a 60 GHz waveband) in order to a high data rate. Technologies such as beamforming, massive Multi-Input Multi-Output massive (MIMO), Full Dimensional MIMO (FD-MIMO), an array antenna, analog beamforming, and a large scale antenna have been discussed for the 5G communication system in order to reduce a path loss of radio waves and increase the transmission distance of radio waves in millimeter wavebands.
Further, technologies such as an improved small cell, an advanced small cell, a Cloud Radio Access Network (could RAN), an ultra-dense network, a Device to Device (D2D) communication, a wireless backhaul, a moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation have been developed for the 5G communication system to improve the network for the system.
In addition, hybrid FSK and QAM modulation (FQAM) and Sliding Window Superposition Coding (SWSC) that use Advanced Coding Modulation (ACM) type, and a Filter Bank Multi Carrier (FBMC), Non Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA) that are advanced connection technologies have been developed for the 5G system.
On the other hand, the internet is evolving from a human-centric network on which people create and consume information to the Internet of Things (IoT) network on which distributed components such as things transmit/receive and process information. The Internet of Everything (IoE) technology may be an example of merging a big data processing technology using connection with a cloud server etc. with the IoT technology.
Technical elements such as a sensing technology, a wire/wireless communication and network infrastructure, a service interface technology, and a security technology are required to achieve the IoT, so, recently, technologies such as a sensor network, a Machine to machine (M2M) communication, and Machine Type Communication (MTC) for connecting between objects are studied.
An intelligent internet technology (IT) service that creates a new value for human life by collecting and analyzing data created from connected objects can be provided in the IoT environment. The IoT can be applied to fields such as a smart home, smart building, a smart city, a smart car or connected car, a smart grid, healthcare, smart appliances, and a high-tech medical service by merging and combining the IT and various industries.
Accordingly, there have been various attempts to applying the 5G communication system to the IoT network. For example, 5G communication technologies such as a sensor network, an object communication, and MTC are implemented by techniques such as beamforming, MIMO, and array antennas. It may be an example of mergence of the 5G technology and the IoT technology to apply a cloud wireless access network as the technology of processing big data described above.
The current mobile communication system is being developed into a high-speed and high-quality wireless packet data communication system for providing a data service and a multimedia service beyond the early stage of providing voice-based services. To this end, several standardization organizations such as 3rd-Generation Partnership Project (3GPP), 3GPP2, and Institute of Electrical and Electronics Engineers (IEEE) have progressed 3rd-generation advanced mobile communication system standardization to which a multiple access method using multi-carriers is applied. Recently, various mobile communication standards such as LTE of 3GPP, Ultra Mobile Broadband (UMB) of 3GPP2, and 802.16m of IEEE have been developed to support a high-speed and high-quality wireless packet data transmission service on the basis of the multiple access method using multi-carriers.
Existing 3rd-generation advanced mobile communication systems such as LTE, UMB, and 802.16m are based on the multi-carrier multiple access method and use MIMO antennas and various technologies such as beamforming, an Adaptive Modulation and Coding (AMC) method, and a channel sensitive scheduling method to improve the transmission efficiency. These technologies improve system capacity performance by improving the transmission efficiency by concentrating transmission power transmitted from several antennas or controlling the amount of data, depending on a channel quality etc., and selectively transmitting data to users having a good channel quality.
Most of these techniques are based on channel state information between an evolved node B (eNB) or a base station (BS) and user equipment (UE) or a mobile station (MS). Accordingly, a base station or a terminal needs to measure the channel station between the base station and the terminal, and for this purpose, a Channel State Information Reference Signal (CSI-RS) may be used. The eNB described above means a downlink transmission and uplink reception device at a predetermined place and one eNB performs transmission and reception for a plurality of cells. In one communication system, a plurality of eNBs is geometrically distributed and each performs transmission and reception for a plurality of cells.
Existing 3rd- and 4th-generation mobile communication systems such as LTE/LTE-Advanced (LTE-A) use a MIMO technology that uses a plurality of transmission and reception antennas for transmission to increase the data rate and the system capacity. The MIMO technology is a technology that spatially separates and transmits a plurality of information streams, using a plurality of transmission and reception antennas. The technique of spatially separating and transmitting a plurality of information streams is called spatial multiplexing. In general, how many information streams spatial multiplexing can be applied depends on the number of antennas of a transmitter and a receiver. In general, the index that shows how many information streams spatial multiplexing can be applied is called the rank of the corresponding transmission. When there are eight transmission and reception antennas, the MIMO technology that is supported under standards including up to LTE/LTE-A Release 11 supports spatial multiplexing, in which maximally up to eight ranks are supported.
Meanwhile, the FD-MIMO technology proposed to improve a network speed and increase frequency efficiency is a technology evolved from the LTE/LTE-A MIMO technology and uses many transmission antennas over eight (for example, thirty two or more transmission antennas).
In order to effectively achieve an FD-MIMO system to which the FD-MIMO technology is applied, a terminal has to accurately measure a channel situation and the intensity of interference and transmit effective channel state information to a base station using the measured factors. The base station receiving the channel state information determines which terminals it performs transmission to in relation to downlink transmission, which speed it performs transmission at, which precoding it applies, etc., using the channel state information. In an FD-MIMO system, there are many transmission antennas and a two-dimensional antenna array is considered, so it is inappropriate to apply a method of transmitting and receiving channel state information about an LTE/LTE-A system designed in consideration of only maximum eight one-dimensional array transmission antennas to the FD-MIMO system, and the problem of uplink overhead that has to transmit additional control information to obtain the same performance is generated.
In the FD-MIMO system, beamforming CSI-RSs are used to reduce the number of CSI-RS ports that a terminal has to measure at a time and overhead for all the CSI-RSs. A base station has to notify a terminal of various Codebook Subset Restrictions (CSR) in order to effectively achieve the beamforming CSI-RSs. However, the CSR is configured by a very large bitmap, so it may be a large burden to configure several CSRs in upper layer signaling such as an RRC message.
Further, when the number of cell specific beams that are supported by cell specific beamforming CSI-RSs or the number of UE specific beams that are supported by UE specific beamforming CSI-RSs is increased, the CSI-RS may be increased larger than a case when non-precoded CSI-RSs are used. A measurement restriction method that limits time sources of CSI-RSs that are measured by a terminal in order to minimize an increase of overhead may be applied to the beamforming CSI-RSs. However, a CSI report that is transmitted through a PUCCH cannot carry RI/W1/W2/CQI at a time for the characteristics of the PUCCH, so they are unavoidably transmitted several times. When the time resource for combining and reporting RI/W1 and W2/CQI with measurement restriction changes, there may be a problem with the reliability of the reported RI/W1.